The invention relates to a trip system for an electrical switch, comprising a yoke of magnetic material, consisting of a yoke base part, a first yoke leg and a second supporting yoke leg, said first and second yoke legs extend in the same direction from the yoke base part, transversely thereto and in mutual spaced relation, an armature from magnetic material, bridging the free ends of the yoke lets and supported pivotably by the supporting yoke leg, a permanent magnetic, provided such that its magnetic field lines extend through a first magnetic circuit formed by the yoke and the armature, a coil mounted on the yoke and spring means engaging the armature, in which the armature is held in a first position under influence of the magnetic field of the permanent magnet against the spring force of the spring means, in which the armature lies against the free end of the first yoke leg and in which the armature can assume a second position under influence of the magnetic field developed by a current flowing through the coil and exceeding a predetermined limit value, in which the surfaces facing to each other of the armature and free end of the first yoke leg at a first air gap distance from each other.
Such a trip system is known from the Dutch patent application 1004438.
Trip systems for electrical switches, for example earth leakage switches, have to serve the purpose to unlock a main switch mechanism biased by springs with minimum switching energy/costs or tuned switching energy, so that the earth leakage switch could be opened.
The above mentioned known trip system operates by unlocking a magnetic circuit closed by means of the permanent magnet. This magnetic circuit is formed by the two-leg yoke, the pivotable armature and the permanent magnet. The armature is arranged pivotable and thereby supported by a supporting yoke leg of the yoke, while between the other yoke leg and the armature an air gap is provided, which can be opened or closed by rotating the armature. The permanent magnet is provided in a recess of the other yoke leg. On one of the two yoke legs a coil is provided. A spring is arranged such between armature and yoke that said spring can provide the air gap opening force on the armature. The permanent magnet provides the air gap closing force. The spring is in the position of the armature in which this lies against the free end face of the first yoke leg, so that in this spring the energy is accumulated, by which a main switch mechanism can be unlocked. The pretension of the spring is just not high enough to remove the force exerted on the armature by the permanent magnetic field in the magnetic circuit and to open the air gap between armature and first yoke leg.
By exciting the winding the magnetic field from the permanent magnet is cancelled partly, by which the spring can open the air gap between armature and first yoke leg and thereby, can deliver the accumulated mechanical energy to a main switch mechanism. Thereby it is achieved that the trip system is unlocked with minimum energy.
This known trip system has, however, still the disadvantage that the more the energy is opened further, the spring detentions, by which the opening force on the armature decreases.
The invention has the object to provide a trip system of the kind mentioned above, in which said disadvantage is obviated, the accuracy of the trip system is further improved and the manufacturing is simplified as much as possible.
This object is achieved according to the invention, in that the magnet is included in a second circuit formed by the yoke and the armature, said circuit having a magnetic resistance in the first position of the armature, which resistance is higher than that of the first magnetic circuit and decreases in the movement of the armature from the first to the second position. Thereby the opening performance of the armature is improved and a more or less force-path-characteristic of the trip system is achieved, when this comes to action.
The magnetic resistance varying dependent on the armature movement compensates for the varying force of the spring means during the armature movement.
The varying magnetic resistance can be achieved by using an air gap in the second magnetic circuit arranged such that this air gap decreases when the spring force of the spring means on the armature decreases during the movement of the armature from the first position to the second position.
In a first embodiment the yoke base part is provided with a yoke base part extension extending beyond the supporting yoke leg and merging into a third yoke leg extending spaced from the supporting yoke leg and in the same direction thereof, in which a permanent magnet is added to the magnetic path of yoke base part extension and a third yoke leg and in which the armature is extended and overlaps the free end face of the assembly of yoke base part extension, third yoke leg and permanent magnet at a second air gap distance, when the armature is in the first position.
In a second embodiment the armature has two legs, the one armature leg of which bridging the space between the first yoke leg and the supporting yoke leg and the second armature leg of which extends transversely to the one armature leg and at a distance from the supporting yoke leg, in which a space remains between the faces facing to each other of the second armature leg and the supporting yoke leg for accommodating the permanent magnet with a second air gap.